WWW.WA S .ORG • WORLD AQUACULTURE • JUNE 2022 67 intestine. Biochar has a strong adsorption or suppression capacity for Gram-negative bacteria with high metabolic activity. Another possible mechanism is the enhanced proliferation of beneficial microbes, particularly species of Bifidobacterium, Enterococcus and Lactobacillus. Biochar decreases toxic substances, creating a competitive environment between beneficial and harmful microbes that directly suppress pathogenic bacteria (Schmidt et al. 2019). Conclusion The increasing demand for fish feed creates new scope for the discovery of unconventional fish feed ingredients but these ingredients may contain harmful substances that negatively affect fish growth and health. Biochar can absorb toxins and anti-nutritional substances in feed. In addition, dietary supplementation of biochar can improve fish growth performance, nutrient utilization, gut morphology, proliferation of beneficial microbes and water quality. Therefore, biochar is an excellent feed additive that can be used to achieve better fish growth and health. ( C O N T I N U E D O N P A G E 6 8 ) antinutritional components such as tannins, phenols, alkaloids, salicylates and thionins. Biochar has a high affinity for binding toxins produced by plants because of its physiochemical characteristics, including its pore network, surface area and surface acidity. The pore structure of the biochar helps to reduce the diffusion of antinutritional substances and the high surface acidity of the biochar has the repulsive effect of the positive charge of some anti-nutritional substances. In addition, biochar adsorbs certain feed and metabolic substances such as tannins, phenols or thionin that are also electron acceptors and may further enhance the electron buffering of biochar particles as they pass through the digestive tract (Schmidt et al. 2019). Elimination of PathogenicBacteria Feeding biochar can stimulate the proliferation of beneficial microorganisms in the gastrointestinal tract and eliminate harmful bacteria. The mechanism associated with the reduction of pathogenic microbes by dietary biochar supplementation is the biochar structural properties like the small pores that trap pathogenic bacteria in the TABLE 1. Selected studies on biochar use as a feed additive in fish feed. Spec ies Biochar Dietary Recommended Resul t Reference source inc lus ion (%) level (%) Giant trevally Rice husk 0, 1, 1.5, 2, 2 Improved growth performance and Firdus et al. Caranx ignobilis 2.5 and 3 nutrient utilization 2021 Enhanced average length and width of foveola gastrica Increase average length and width of intestinal villi Red tilapia Wood 0, 1 and 2 1 Increase specific growth rate and relative Samson Oreochromis niloticus growth rate 2019 Common carp Bamboo 0, 0.5, 1, 2 4 Improves serum parameters Mabe et al. Cyprinus carpio and 4 Improving the intestinal villus length and 2018 goblet cells numbers Brown trout Not 0, 0.1, 0.2 0.2 Increase weight gain, SGR and FCR Khaki et al. Salmo trutta specified and 0.3 Improved survival 2017 Striped catfish Rice 0 and 1 1 Increase growth performance Lan et al. Pangasius hypophthalmus husk Improved gut microbiota status 2016 Enhanced water quality parameters Striped catfish Bamboo 0, 0.5, 1 2 Improvement in growth performance Quaiyum et al. Pangasius hypophthalmus and 2 and water quality 2014 Increase height and area of intestinal villus segments Olive flounder Bamboo 0, 0.25, 0.5, 1, 0.5-1 Enhanced growth performance and Thu et al Paralichthys olivaceus 2 and 4 nutrient utilization 2010 Reduced ammonia nitrogen excretion Tiger puffer fish Bamboo 0, 0.004, 0.01, 4 Improved growth performance and Moe et al. Takifugu rubripes 0.1, 1 and 4 nutrient utilization 2009 Increase nitrogen retention Reduced nitrogen excretion Olive flounder Wood 0, 0.5, 1, 1.5 1 Increase weight gain and feed efficiency Yoo et al. Paralichthys olivaceus and 2 Lower whole-body lipid 2005
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